Definition of Kingdom Protista

The kingdom Protista or Protista is one of the five kingdoms in the ancient classification of beings. living, which, although it has become obsolete for biology, still retains didactic value for its simplicity. There are a wide variety of organisms in the kingdom Protista, from single-celled forms to giant algae that form vast forests in the oceans. The kingdom protista groups all the eukaryotic organisms, unicellular or multicellular that could not be located within the other known eukaryotic kingdoms: Fungi, Plantae and Animalia.

Over time, and as knowledge of the biology of these groups of organisms progressed, it became increasingly evident that the Organisms included in the kingdom Protista were not related to each other, and some of them would be better classified as plants or fungi. At present, the name protists continues to be used as a way of referring to these simple eukaryotic organisms and the kingdom classification has been superseded by a complete classification of eukaryotes based on molecular biology. In this article we will refer to the large groups of organisms traditionally grouped as protists.

Characteristics of protists

It is a group of organisms that has a great diversity of forms and finding characteristics shared by all of them is really difficult. Perhaps their only characteristic in common is that they are organisms with eukaryotic cells, that is, with a nucleus and organelles delimited by membranes. Most are unicellular or form colonies (a colony is the grouping of many organisms, but each of them continues to have complete autonomy. In other words: each of the cells in a colony is still a complete organism, unlike the true multicellularity in which only the set of cells forms the organism and one cell separate from the rest go dead). There are also some multicellular protists, but their cells are not specialized and do not form true tissues (as occurs in plants and animals).

Classification of protisats

Protists are divided into different groups according to their morphology, anatomy and way of life, they can be autotrophs or heterotrophs. Autotrophs are traditionally known as “algae”, while heterotrophs are known as “protozoa”.

Algae

Algae are photosynthetic organisms, they live in both fresh and salt water, but they are much more abundant in the sea. All photosynthetic organisms have chlorophyll, which is essential for photosynthesis to occur. Some algae only have chlorophyll and are therefore green. There are other groups of algae, also photosynthetic, that have other pigments in addition to chlorophyll. These additional pigments give them brown and reddish colors, and red algae, brown algae, and golden algae are recognized by this characteristic.

Among the algae, there is a wide variety of unicellular organisms, which are common components of marine and lake phytoplankton, and large multicellular organisms. dimensions, such as the brown algae known as sargassum and kelps, which are washed up by the waves and end up on the beaches forming piles of decomposed seaweed with badly smell. These giant kelp form veritable forests in the oceans, which provide habitat for many other species. These unique ecosystems depend on these giant algae to survive.

In aquatic ecosystems, especially marine ones, algae are the main producers in trophic chains, since in There are no plants in the ocean, and few plants are adapted to living completely submerged in shallow water, close to the sea. coast. Some green and brown algae are used as food in some culinary traditions, especially in coastal Asian countries.

Green algae have great evolutionary importance, since land plants descend from them.

protozoa

Protozoa are heterotrophic unicellular organisms. Like algae, there are a wide variety of organisms grouped together as protozoa and they are found in a variety of aquatic and terrestrial environments.

The vast majority of them are unicellular and can move by different mechanisms. This ability to move on their own made them, in the past, more closely related to animals. One of the traditional classifications of protozoa groups them based on the movement mechanisms they use. This classification proposes the following groups:

The ciliates, which use cilia, a kind of "hair" on the cell to swim. The cilia beat in sync, propelling the cell by creating a current of water. It is somewhat similar to rowing competitions, in which all rowers row synchronously. Some of the best known protozoa, such as the paramecium, are ciliates.

flagellates have flagella, which are structurally the same as cilia, but longer and whip-like. The movement of these protozoa is more abrupt, and sometimes the cell advances by “bumping”.

The other groups of protozoa are the amoebas, which move by means of pseudopods, which are "protrusions" that the cell emits and give the impression that the organism "flowed" over the surface. Finally, the sporozoans, which are completely motionless.

All protozoa are heterotrophs and ingest their food, but some are parasitic and cause serious disease in animals. people, such as Chagas (caused by a flagellate), malaria or paludism or amoebic dysentery (caused by a amoeba). These parasites are usually transmitted by insect bites or by ingesting contaminated food or water. Most protozoan species are harmless to humans and do not cause problems.